The invention relates to a moulding tool for a machine for processing glass or other plastic material, the tool comprising at least one mould middle section divided into middle section parts, and an operating device having members each carrying with clearance a respective one of the mould middle section parts for opening and closing movements transversely of the longitudinal axis of the respective mould and transversely guiding the parts in two spaced guide planes by means of guide elements.
A known moulding tool of this kind (West German Offenlegungsschrift 2,355,030) comprises a multiple mould with which appertaining mould middle section halves are respectively on their outside provided with a downwardly extending flange at their upper end and, approximately in half their longitudinal extension, with a headed screw. The flange, with radial clearance, is suspended on a suspension console of a tong half forming the operating device. A head of the headed screw, with radial clearance, engages downwardly in a groove of the tong half. Thus two radial guide planes are defined. The mould middle section halves are not secured in the axial direction and so under unfavorable operating conditions can be lifted upwardly and fall out of the operating device. Two pressure members of the appertaining tong half engage each mould middle section half, whereby two axial holding closed force zones are defined. The pressure members are arranged in spaced relationship and one above the other respectively below one of said two guide planes.
The object of this known moulding tool is to exert to the mould middle sections of all the individual moulds of said multiple mould a holding closed force of like magnitude. To this end all the pressure members of each tong half are constantly connected to each other via a closed hydraulic channel system, so that, when the moulding tool is firmly closed, each pressure member exerts a holding closed force of like magnitude to the appertaining mould middle section. In this condition the mould middle section halves shall be held by the tong halves freely movably in the radial direction and "floatingly." A disadvantage is that the line of action of the holding closed force resulting from both the pressure members of each mould middle section half does not coincide with the line of action of the resultant opening force acting on the respective mould middle section half. That is why it is known to happen that the mould middle section will open either at its top or at its bottom and split apart obliquely under the internal pressure existing during the processing. This results in the formation of more or less coarse seams on the parisons and on the finished hollow glass products. These seams are unsightly and degrade the strength and quality of the product. They can also result in rejected articles, in particular at the finishing mould stage. Furthermore the tendency to split open involves unequal wear of the mould middle sections. On account of the mould cracking or splitting it is not possible to produce all types of hollow glass articles with the known moulding tools.
Another disadvantage is that the radially "floating" suspension of the mould middle sections on the tongs precludes centering of the mould middle sections with respect to the remainder of the moulding tool. This may lead to uneven production and increased wear of the moulding tool.
With the known moulding tool the holding closed force is applied by the tongs. If the tong halves are not absolutely parallel to the longitudinal axes of the individual moulds, oblique and edgewise contacting of the pressure members and the mould middle sections and, with the piston-like pressure members, jamming between the pressure members and their cylinders may occur. This again enhances the wear and creates the danger of leakages in the hydraulic system resulting in the loss of the critical preadjustment thereof. Said preadjustment and consequently desired functioning of the known moulding tool are also endangered by the continuous operational temperature changes of the moulding tool.
When the machine is in operation, due to the occurrence of irregular thermal loads, e.g. during the starting up of the machine, correspondingly irregular thermal expansion takes place of the mould middle section and the operating device, so that correspondingly wide tolerances must be available in the means for suspension and guidance between the mould middle section and the operating device. At the times when the mould middle sections are not securely closed, the effect of these tolerances is to allow varying oscillations of the mould middle sections about a transverse axis with respect to the operating device, and wear between these parts caused by the resulting impacts. This again increases the machine noise. These disadvantages further accumulate as the production speed increases.